Abstract
AbstractQuantification of allogenic controls in rift basin‐fills requires analysis of multiple depositional systems because of marked along‐strike changes in depositional architecture. Here, we compare two coeval Early‐Middle Pleistocene syn‐rift fan deltas that sit 6 km apart in the hangingwall of the Pirgaki‐Mamoussia Fault, along the southern margin of the Gulf of Corinth, Greece. The Selinous fan delta is located near the fault tip and the Kerinitis fan delta towards the fault centre. Selinous and Kerinitis have comparable overall aggradational stacking patterns. Selinous comprises 15 cyclic stratal units (ca. 25 m thick), whereas at Kerinitis 11 (ca. 60 m thick) are present. Eight facies associations are identified. Fluvial and shallow water facies dominate the major stratal units in the topset region, with shelfal fine‐grained facies constituting ca. 2 m thick intervals between major topset units and thick conglomeratic foresets building down‐dip. It is possible to quantify delta build times (Selinous: 615 kyr; Kerinitis: >450 kyr) and average subsidence and equivalent sedimentation rates (Selinous: 0.65 m/kyr; Kerinitis: >1.77 m/kyr). The presence of sequence boundaries at Selinous, but their absence at Kerinitis, enables sensitivity analysis of the most uncertain variables using a numerical model, ‘Syn‐Strat’, supported by an independent unit thickness extrapolation method. Our study has three broad outcomes: (a) the first estimate of lake level change amplitude in Lake Corinth for the Early‐Middle Pleistocene (10–15 m), which can aid regional palaeoclimate studies and inform broader climate‐system models; (b) demonstration of two complementary methods to quantify faulting and base level signals in the stratigraphic record—forward modelling with Syn‐Strat and a unit thickness extrapolation—which can be applied to other rift basin‐fills; and (c) a quantitative approach to the analysis of stacking patterns and key surfaces that could be applied to stratigraphic pinch‐out assessment and cross‐hole correlations in reservoir analysis.
Highlights
Distinguishing faulting, sediment supply and base level signals and quantifying these basin controls in an active rift setting remains problematic, due to along-strike variability in depositional architecture
Previous work on the stratigraphic record around normal faults at rifted margins has focussed on the theoretical aspects of sequence development from the interplay of controls in these areas
At Kerinitis, our study focuses on three down-dip locations over ~700 m, covering the lower-middle units of the delta: K1a, b, c - Units 4 and 7, K2 - Units 5 and 6, and K3 - Units 2 and 3
Summary
Distinguishing faulting, sediment supply and base level signals and quantifying these basin controls in an active rift setting remains problematic, due to along-strike variability in depositional architecture. Characterisation of multiple coeval depositional systems within the same rift basin is required to resolve the record of each control. Syn-rift, Gilbert-type fan deltas (Gilbert, 1885, 1890) provide an ideal record of stratigraphic evolution to achieve this due to their position adjacent to normal growth faults, with high and variable sediment supply rates derived from independent drainage catchments. Previous work on the stratigraphic record around normal faults at rifted margins has focussed on the theoretical aspects of sequence development from the interplay of controls in these areas. An influential series of conceptual models for tectonosedimentary evolution in extensional basins was presented by Gawthorpe & Leeder (2000)
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